Pilot-scale comparison of sodium silicates, orthophosphate and pH adjustment to reduce lead release from lead service lines

WATER RESEARCH

卷:195

Article

Aghasadeghi, Kimia¹  Peldszus, Sigrid¹  Trueman, Benjamin F.²  Mishrra, Anushka³  Cooke, Mitchell G.⁴  Slawson, Robin M.⁴  Giammar, Daniel E.³  Gagnon, Graham A.²  Huck, Peter M.¹ 

[1] Univ Waterloo, Dept Civil & Environm Engn, 200 Univ Av W, Waterloo, ON N2L 3G1, Canada

[2] Dalhousie Univ, Dept Civil & Resource Engn, Halifax, NS B3H 4R2, Canada

[3] Washington Univ, Dept Energy Environm & Chem Engn, St Louis, MO 63130 USA

[4] Wilfrid Laurier Univ, Dept Biol, Waterloo, ON N2L 3C5, Canada

关键词: Lead corrosion;    water treatment;    sodium silicate;    orthophosphate;    pH adjustment;    lead service line;   

DOI  :  10.1016/j.watres.2021.116955

来源: Elsevier

【 摘 要 】

Sodium silicate is thought to mitigate lead release via two mechanisms: by increasing pH and by forming a protective silica film. A pilot-scale study using an excavated lead service line (LSL) fed with water from a Great Lakes source was undertaken to: (1) clearly distinguish the pH effect and the silica effect; (2) compare sodium silicate to orthophosphate and pH adjustment; (3) determine the nature of silica accumulation in the pipe scale. The LSL was cut into segments and acclimated with water at pH 7.1. Median dissolved lead was 197 mu g/L in the last 8 weeks of acclimation and dropped to 16 mu g/L, 54 mu g/L, and 85 mu g/L following treatment with orthophosphate (dose: 2.6 mg-PO4/L, pH: 7.9), pH adjustment (pH: 7.9) and sodium silicate (dose: 20 mg-SiO2/L, pH: 7.9), respectively. When silica dose was increased from 20 mg-SiO2/L to 25 mg-SiO2/L (pH: 8.1), lead release destabilized and increased (median dissolved lead: 141 mu g/L) due to formation of colloidal dispersions composed mainly of lead- and aluminum-rich phases as detected by field flow fractionation used with inductively coupled plasma mass spectrometry. Si was present in the scale at a maximum of 2.2 atomic % after 17 weeks of silica dosing at 20 mg-SiO2/L. Under the conditions tested, sodium silicate did not offer any benefits for reducing lead release from this LSL other than increasing pH. However, sodium silicate resulted in lower levels of biofilm accumulation on pipe walls, as measured by heterotrophic plate counts, when compared to orthophosphate. (C) 2021 The Authors. Published by Elsevier Ltd.

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